You didn't mention what brand dishwaser you are talking about, but if it is a Bosch, they are known for having the impeller (which is in 2 parts) coming apart, so the part of the impeller that has the blades doesn't turn. In other dishwashers, I've seen the holes in the wash arms get clogged, especially if you don't have the removable filter installed correctly, or (if it's a GE), the filter plate on the bottom gets warped, allowing bood and debris to get in the wash arms and clog up the holes. We really need to know the brand and model number of the dishwasher (or any appliance) to be able to help you accurately.